Anatomical investigation of potential contacts between climbing fibers and cerebellar Golgi cells in the mouse

Elisa Galliano,Freek E Hoebeek,Chris I De Zeeuw,Martina Sgritta,Elize D Haasdijk,Egidio D'Angelo,Marco Baratella,Tom J H Ruigrok,Dick Jaarsma

doi:10.3389/fncir.2013.00059

Abstract

Climbing fibers (CFs) originating in the inferior olive (IO) constitute one of the main inputs to the cerebellum. In the mammalian cerebellar cortex each of them climbs into the dendritic tree of up to 10 Purkinje cells (PCs) where they make hundreds of synaptic contacts and elicit the so-called all-or-none complex spikes controlling the output. While it has been proven that CFs contact molecular layer interneurons (MLIs) via spillover mechanisms, it remains to be elucidated to what extent CFs contact the main type of interneuron in the granular layer, i.e., the Golgi cells (GoCs). This issue is particularly relevant, because direct contacts would imply that CFs can also control computations at the input stage of the cerebellar cortical network. Here, we performed a systematic morphological investigation of labeled CFs and GoCs at the light microscopic level following their path and localization through the neuropil in both the granular and molecular layer. Whereas in the molecular layer the appositions of CFs to PCs and MLIs were prominent and numerous, those to cell-bodies and dendrites of GoCs in both the granular layer and molecular layer were virtually absent. Our results argue against the functional significance of direct synaptic contacts between CFs and interneurons at the input stage, but support those at the output stage.

Highlights

The olivo-cerebellar system is believed to be an online comparator that calculates the difference between a desired and an executed movement via its highly organized and preserved cellular network and forwards the appropriate modification through its projections to the brainstem (Marr, 1969; Albus, 1971)
When we quantified the number of vesicular glutamate transporter type 2 (VGluT2) stained terminals on top of DAPI stained cell-bodies of molecular layer interneurons (MLIs)’s (n = 550), we found that 61.3% showed a co-localization using the same criteria
These data did not provide any evidence of synaptic contacts in the ML layer between metabotropic glutamate receptor type 2 (mGluR2)-positive Golgi cells (GoCs) and VGlut2-containing climbing fibers (CFs), whereas they provided robust evidence for appositions of CFs onto Purkinje cells (PCs) and MLIs

Summary

Introduction

The olivo-cerebellar system is believed to be an online comparator that calculates the difference between a desired and an executed movement via its highly organized and preserved cellular network and forwards the appropriate modification through its projections to the brainstem (Marr, 1969; Albus, 1971). Information about the desired and executed behavior reaches the cerebellar cortex via two main types of fibers. These are the so-called climbing fibers (CFs), which all originate from the inferior olivary nucleus (IO), and the mossy fibers (MFs), which can be derived from many other sources in the brainstem (Ramon y Cajal, 1995). Single CFs make direct and numerous synaptic contacts with PCs. A classical model of cerebellar functioning postulates that the CFs provide the required error signals encoding the difference between the executed and desired movement and thereby guide motor learning (Marr, 1969; Albus, 1971). We injected a fluorescent anterograde tracer in the IO in mutant mice that express eGFP in their glycinergic neurons (GlyT2eGFP) so as to enable immunofluorescent identification of both

Methods

Results

Conclusion